1. Field of the Invention
The present invention relates to an audio and video processing apparatus which performs decompression of compressed video and audio data, compression of video and audio data, graphics processing, and the like.
2. Discussion of the Related Art
In recent years the art of compression and decompression of digital moving image data has become established, and the LSI art has also improved; and various types of audio and video processing apparatus such as decoders for decompressing compressed video and audio data, encoders for compressing video and audio data, graphics processing devices for performing graphics processing, and the like have gained in importance.
As one prior art, there is a type of audio and video processing apparatus which decompresses a video and audio stream which have been compressed according to the DVD-Video standard. Audio signals known in this DVD-Video standard are generally stored in the linear 16 bit 2 channel PCM format at the sampling frequency of 48 kHz, and the data quantity for the video signal is overwhelmingly greater than the quantity for the audio signal. Along with the improvement of the LSI art, there are nowadays various versions of such audio and video processing apparatus which have been LSI-integrated onto a single chip. Among such audio and video processing apparatus, a typical example of an audio and video processing apparatus which decompresses compressed video and audio streams in the DVD-Video standard, is shown in FIG. 1 of the drawings.
A main section 1000 of this audio and video processing apparatus includes an input and output processing section 1100, a decode processing section 1200, and a memory controller 1300, and it is connected to an external memory 1400. The input and output processing section 1100 is made up of a stream input section 1110 which inputs a program stream from external devices, a buffer memory 1120 which serves as an internal buffer during data transfer, and an I/O processor 1140 which operates while changing over between a plurality of task means. The decode processing section 1200 is made up of a first in first out (hereinafter abbreviated as “FIFO”) memory 1210, a video processing section 1220 which decodes the video stream, and an audio processing section 1230 which decodes the audio stream. The FIFO memory 1210 includes a video stream FIFO 1211 which transfers the video stream to the video processing section 1220, and an audio stream FIFO 1212 which transfers the audio stream to the audio processing section 1230. And the memory controller 1300, performs data input and output between the main section 1000 and the external memory 1400.
Further, the external memory 1400, which is connected externally, is allocated between a buffer area 1410 for video and a buffer area 1420 for audio.
Moreover, the stream parsing means 1141 in the I/O processor 1140 divides the data stream which has been inputted by the stream input section 1110 and has been transferred to the internal buffer memory 1120 into audio and video streams, and commands the memory controller 1130 to transfer the data to the buffer areas 1400 and 1410 for video and audio within the external memory 1400. The video buffer control means 1142 performs transfer of the video stream from the buffer area 1410 for video to the video stream FIFO 1211. And the audio buffer control means 1143 performs transfer of the audio stream from the audio buffer area 1420 to the audio stream FIFO 1212.
As shown in FIG. 1, first, when a program stream according to the DVD-Video standard is input from the stream input section 1110, the stream parsing means 1141 of the I/O processor 1140 divides it into a video stream and an encoded signal for audio. And, via the memory controller 1300, the encoded signal for video is transferred to the video buffer area 1410, while the encoded signal for audio is transferred to the audio buffer area 1420. Next, the video buffer control means 1142 transfers the video stream to the video stream FIFO 1211 from the video buffer area 1410 in response to a stream supply request from the video processing section 1220. The audio buffer control means 1143 transfers the audio stream to the audio stream FIFO 1212 from the audio buffer area 1420 in response to a stream supply request from the audio processing section 1230. The video processing section 1220 receives the video stream signal from the video stream FIFO 1211, performs decoding thereof, and generates a video output signal. And the audio processing section 1230 receives the audio stream signal from the audio stream FIFO 1212, performs decoding thereof, and generates an audio output signal.
Most of such audio and video processing apparatus, the video stream conforms to the DVD-Video standard, and generally contains a moving image. In this case, the amount of data in the video stream which is contained in the program stream is remarkably greater as compared to the audio stream, and almost always the amount of processing required for decoding the video stream is greater than that required for decoding the audio stream. For example, it is almost always the case that the data transfer processing capacity of the video buffer control means 1142 is remarkably greater by comparison with that of the audio buffer control means 1143. Furthermore, in the decode processing section 1200, the processing priority level accorded to the video processing section 1220 is higher than that accorded to the audio processing section 1230. In the DVD-Video standard, most audio signals, which are of the linear PCM format, contain a level of information roughly equal to that of a compact disk, and are 2 channel 16 bit linear PCM signals sampled at 48 kHz.
However, with an audio and video processing apparatus of this type, the video processing section and the audio processing section are independent and individually established in advance. Further as another video standard, there is the known DVD-Audio standard, with which, for the video and audio input, the ratios of the transfer amounts of encoded signals and of decode calculation amounts greatly differ from those of a program stream according to the DVD-Video standard. Since with this format the amount of information in the audio signal is increased so as to enable higher quality sound reproduction, six channel 24 bit linear PCM with sampling frequency of 96 kHz, or two channel 24 bit linear PCM with sampling frequency of 192 kHz, may be selected. In this case, the video signal displays still images at fixed intervals. If an audio and video processing apparatus is to serve for processing a program stream according to the DVD-Audio standard as well as to the DVD-Video standard, then the data transfer capability of the audio buffer control means and the calculation processing capability of the audio processing section must be higher than in the case of decoding a program stream according to the DVD-Video standard. In order to provide this enhanced capability, circuit complexity and clock speed must be increased, and as a result cost and power consumption undesirably increase.